Industry accepted system installation standards and definitions for storage fire protection are provided in National Fire Protection Association publication, NFPA 13: Standard for the Installation of Sprinkler Systems (2013 ed.) (“NFPA 13”). Chapters 11-12 define standardized hydraulic design approaches for systems designed and installed with “automatic” storage sprinklers, such as for example, standard spray, control mode specific application (CMSA), extended coverage or early suppression fast response (ESFR). NFPA 13 defines “automatic sprinklers” as “a fire suppression or control device that operates automatically when its heat-activated element is heated to its thermal rating or above, allowing water to discharge over a specified area.” As used herein, a “hydraulically designed system,” is a calculated system in which pipe sizes are selected on a pressure loss basis to provide a prescribed water density, in gallons per minute per square foot, or a prescribed minimum discharge pressure or flow per sprinkler, distributed with a reasonable degree of uniformity over a specified area. The standards specify the hydraulic design area or sprinkler operational area, the density (GPM/SQ. FT) requirements, and/or minimum operating pressures for a given storage commodity and arrangement. A “hydraulic design area” is an area, defined in square units of measure, comprising a defined number of hydraulically remote sprinklers at a defined spacing between each sprinkler. “Hydraulically remote sprinklers” are sprinklers that place the greatest water demand on a system in order to provide a prescribed minimum discharge pressure or flow. It is understood by those skilled in the art that the hydraulically remote sprinklers may or may not be physically located the furthest from the fluid the water supply providing the prescribed minimum pressure or flow.
Chapter 21 of NFPA 13 provides for special approaches that permit hydraulic designs other than those specified under Chapters 11-20. According to Section 21.1.8, the hydraulic design area can be defined by a number of design sprinklers as derived from worst-case results obtained from full-scale fire testing. However, regardless of the fire test results, the special design approaches of NFPA still include minimum design requirements. For example, Section 21.1.8.1 requires that the number of design sprinklers defining the hydraulic demand be no less than: (i) twelve sprinklers for standard coverage sprinklers; (ii) eight sprinklers for extended coverage sprinklers on 12 ft.×12 ft. sprinkler-to-sprinkle spacing; or (iii) six sprinklers for extended coverage sprinklers based on 14 ft.×14 ft. sprinkler-to-sprinkler spacing. Moreover, Section 21.1.8.2 provides that the minimum operating area based on the sprinkler-to-sprinkler spacing of the given number of design sprinklers shall be no less than 768 square feet. Other industry accepted standards, for example standards under FM Global (FM), define the number of design sprinklers for use in sprinkler systems for a storage occupancy based upon sprinkler orifice size, orientation, RTI (thermal response), spacing, and minimum operating pressure. Additionally, the number of sprinklers is determined by a fire test in which an appropriate safety factor is assessed on the total number of sprinklers that operate, such as for example, a 50% safety factor. The safety factor is designed to account for uncertainty in the operation sequence inherent to thermo-mechanically operated automatic sprinkler systems due to things such as sprinkler skipping, fire chasing, etc. The hydraulic designs and demand of the system define the water supply requirements of the system and the economic burden to fulfill those requirements, such as for example, by supplying the appropriate number and size of pump, piping or other fluid distribution equipment to meet the hydraulic designs. Accordingly, there is a desired balance between fulfilling a level of hydraulic demand and the economic burden to supply that demand in order to provide a desired level of fire protection. Generally, it is advantageous to minimize the hydraulic design area and/or number of design sprinklers of a system in order to reduce the overall hydraulic demand of the system in order to strike the appropriate balance.
In addition to specifying hydraulic design requirements, the installation standards also include location requirements for the automatic sprinklers. Automatic sprinklers are located above the stored commodity at or near the ceiling of the occupancy in order that its heat-activated element can be activated by the air/gases heated by a fire in the occupancy. Section 8.12.4 of NFPA 13 also includes “distance below ceiling” requirements to locate the deflector of the automatic sprinkler below the ceiling of the storage occupancy. According to the standards, a deflector of a pendent sprinkler is to be located at a maximum of 18 inches from the ceiling. The construction of the storage occupancy, particularly at or near the ceiling, can present obstructions to the spray pattern of a sprinkler, obstructions can include for example, beams, ducts, lights, trusses or bar joists at or near the ceiling. Accordingly, the installation standards provide for obstruction standards. Section 8.12.5 of NFPA 13 includes obstruction rules or requirements for Early Suppression Fast-Response Sprinklers to ensure that the sprinkler and its spray are clear of obstructions at or near the ceiling. The obstruction standards provide for a maximum allowable distance of the deflector above the bottom of the obstruction based upon the distance of the sprinkler from the side of the obstruction. Accordingly, both the structure of the automatic sprinkler and the existing installation standards can limit or restrict the ability to install a sprinkler above a stored commodity at increased distances from the ceiling which can add a burden to installing a system to provide a desired level of fire protection.
Thus, known fire protection systems that employ automatic sprinklers to protect storage occupancies have hydraulic and installation limitations that can add to the overall economic burden to provide the desired level of fire protection. It is therefore desirable to have systems and methods that can reduce the hydraulic demand of a system and/or provide an installation flexibility to provide fire protection for storage occupancies.